1,720,984 research outputs found
Physical Layer Aware Optical Networks
Full text linkThis thesis describes novel contributions in the field of physical layer aware optical networks. IP traffic increase and revenue compression in the Telecom
industry is putting a lot of pressure on the optical community to develop novel solutions that must both increase total capacity while being cost effective. This requirement is pushing operators towards network disaggregation, where optical network infrastructure is built by mix and match different physical layer technologies from different vendors. In such a novel context, every equipment and transmission technique at the physical layer impacts the overall network behavior. Hence, methods giving quantitative evaluations of individual merit of physical layer equipment at network level are a
firm request during network design phases as well as during network lifetime. Therefore, physical layer awareness in network design and operation is fundamental to fairly assess the potentialities, and exploit the capabilities of different technologies. From this perspective, propagation impairments modeling is essential. In this work propagation impairments in transparent optical networks are summarized, with a special focus on nonlinear effects. The Gaussian Noise model is reviewed, then extended for wideband scenarios. To do so, the impact of polarization mode dispersion on nonlinear interference (NLI) generation is assessed for the first time through simulation, showing its negligible impact on NLI generation. Thanks to this result, the Gaussian Noise model is generalized to assess the impact of space and frequency amplitude variations along the fiber, mainly due to stimulated Raman scattering, on NLI generation. The proposed Generalized GN (GGN) model is experimentally validated on
a setup with commercial linecards, compared with other modeling options, and an example of application is shown. Then, network-level power optimization strategies are discussed, and
the Locally Optimization Global Optimization (LOGO) approach reviewed. After that, a novel framework of analysis for optical networks that leverages detailed propagation impairment modeling called the Statistical Network Assessment Process (SNAP) is presented. SNAP is motivated by the need of having a general framework to assess the impact of different physical layer technologies on network performance, without relying on rigid optimization approaches, that are not well-suited for technology comparison. Several examples of applications of SNAP are given, including comparisons of transceivers, amplifiers and node technologies. SNAP is also used to highlight topological bottlenecks in progressively loaded network scenarios and to derive possible solutions for them.
The final work presented in this thesis is related to the implementation of a vendor agnostic quality of transmission estimator for multi-vendor optical networks developed in the context of the Physical Simulation Environment group of the Telecom Infra Project. The implementation of a module based on the GN model is briefly described, then results of a multi-vendor experimental validation performed in collaboration with Microsoft are shown
Raman Crosstalk Suppression in NG-PON2 Using Optimized Spectral Shaping
Full text linkIn this paper, we present an innovative proposal to mitigate the effect of Raman crosstalk in the interaction between NG-PON2 TWDM-PON channels and legacy RF-video by electrical spectral shaping on the TWDM NRZ data stream obtained through electrical FIR filtering. We find an analytical and closed form solution on FIR filter taps that, for a given target spectral shaping, gives the absolute minimum amount of intersymbol interference on the TWDM data. Then, we propose techniques to implement these FIR filters with reasonable system complexity. We found that our proposed technique is applicable to all classes (up to E2 PON, +11 dBm transmitted downstream power) with less than 0.5 dB power penalty on TWDM channels even in the worst-case scenario of RF-video still based on analog channels on the lower part of the spectru
Elastic All-Optical Networks: A New Paradigm Enabled by the Physical Layer. How to Optimize Network Performances?
Full text linkPhysical layer equipment is the enabling technology for the elastic use of networks. We propose the statistical network assessment process as benchmarking method. As an example we compare PM-mQAM vs. TDHMF transceivers on a Pan-EU network topology, considering three fibers
Potentialities and criticalities of flexible-rate transponders in DWDM networks: A statistical approach
Full text linkWe propose a novel method to assess physical layer potentialities of core optical networks aimed at finding solutions that better exploit the installed equipment. We focus on the use of flexible-rate transponders for the implementation of the elastic paradigm on the state-of-the-art dense wavelength-division-multiplexed fixed-grid network scenarios. We make use of the waveplane-based routing and wavelength assignment algorithm presented in Dai et al. [J. Lightwave Technol. , vol. 33, p. 3815, 2015 ] to implement a progressive statistical loading of the analyzed network topology, and perform a Monte Carlo analysis delivering a statistical characterization of the average bit rate per lightpath together with the assessment of network blocking. The proposed method allows for the identification of criticalities in terms of link congestion and lightpath quality of transmission, addressing solutions by identifying network bottlenecks. We apply the proposed method to a large pan-European network topology comparing two different transmission techniques for the implementations of flexible-rate transponders: pure PM-m-QAM versus hybrid modulation formats. Over this realistic network example, besides displaying the overall statistics for the average bit rate per lightpath, we show statistics for critical lightpaths and congested fiber link
Observing the effect of polarization mode dispersion on nonlinear interference generation in wide-band optical links
Full text linkWith the extension of the spectral exploitation of optical fibers beyond the C-band, accurate modeling and simulation of nonlinear interference (NLI) generation is of the utmost performance. Models and numerical simulation tools rely on the widely used Manakov equation (ME): however, this approach when also considering the effect of polarization mode dispersion (PMD) is formally valid only over a narrow optical bandwidth. In order to analyze the range of validity of the ME and its applicability to future wide-band systems, we present numerical simulations, showing the interplay between NLI generation and PMD over long dispersion-uncompensated optical links, using coherent polarization division multiplexing (PDM) quadrature amplitude modulation (QAM) formats. Using a Monte-Carlo analysis of different PMD realizations based on the coupled nonlinear Schrödinger equations, we show that PMD has a negligible effect on NLI generation, independently from the total system bandwidth. Based on this, we give strong numerical evidence that the ME can be safely used to estimate NLI generation well beyond its bandwidth of validity that is limited to the PMD coherence bandwidth
Physical Layer Strategies to Save Lightpath Regenerators
No full textWe investigate the viability of hybrid fiber
amplifiers (HFA) and advanced digital signal processing
(DSP)-based transceivers in translucent optical networks.
We focus on the reduction of optical-electro-optical (OEO)
regenerators required to support a 200 Gbps any-to-any
traffic. In this paper, two network topologies, PanEuropean and USNET, are quantitatively analyzed according to three different upgrade strategies. The first upgrade
strategy includes selective placement of HFA in a network
using different Raman amplification levels. The second upgrade strategy includes the use of two different DSP techniques of digital backpropagation and probability shaping
(PS) at the transceivers. The third upgrade strategy
involves a combination of both HFA and DSP techniques
in a network. Our results indicate that by using these
upgradation strategies, a prominent reduction in OEO
regenerators can be obtained, which can lead to full
transparency of a network. In the Pan-European topology,
improving the equivalent noise figure (ENF) of the optical
amplifiers by 5 dB, it is possible to reduce by 74% the
amount of required regenerators. Then, by applying
advanced DSP techniques like PS, this percentage grows
up to 82%. In the USNET topology, by reducing the ENF
by 2 dB, it is possible to reach full transparency. By using
PS, it is enough to reduce the ENF by just 0.5 dB to reach the
same results
Polarization-Related Statistics of Raman Crosstalk in Single-Mode Optical Fibers
Full text linkWe present a novel comprehensive theory for the pump-to-probe interactions caused by the stimulated Raman scattering (SRS) in glass optical fibers. The developed theory applies to both theRaman gainwith the undepleted pump assumption, and to themaximum loss induced by the Raman crosstalk (RXT loss). The latter is an effect that is the limiting propagation impairment in passive optical networks (PON). The main novelty of the paper is a rigorous mathematical analysis, describing the interaction of SRS with the polarization evolution due to polarization mode dispersion (PMD). The Raman gain (or the RXT loss) is modeled as a random process for which a comprehensive theory is developed, giving for the first time to our best knowledge, an exact closed-form expression for the mean and variance of the gain (or depletion), and a computationally efficient algorithm to numerically derive the gain probability density function. The developed theory is validated by the comparison with Monte Carlo analyses, based on the waveplate model for the optical fiber. The validation showed excellent agreement, confirming the validity of the developed theory. As an example of application, we used our theoretical results to analyze next-generation PON (NG-PON2) architectures, confirming that, in this scenario, RXT loss may be a limiting propagation effec
A statistical analysis of transparent optical networks comparing merit of fiber types and elastic transceivers
Full text linkWe perform a benchmarking of three different fiber types and two different implementation of flexible rate transceivers in a fixed-grid reconfigurable transparent optical network scenario. Results are obtained through a Monte Carlo based method called the Statistical Network Assessment Process (SNAP). Using the SNAP framework, we derive the statistics of the average bitrate per lightpath on a Pan European network scenario. We consider the average of such metric as a unique merit parameter to compare the use SMF, PSCF or NZDSF. We also consider two different implementations of elastic transceivers, namely one based on pure PM-M-QAM and the other using Time Division Hybrid Modulation Formats (TDHMF). TDHMF always outperforms PM-M-QAM, of 23% in SMF and PSCF and of 27% in the poorer transmission quality NZDSF. Results show that using flexible PM-M-QAM, PSCF are able to support a capacity increase in terms of average bitrate per LP of 48% with respect to NZDSF, while the improvement granted by SMF is 34%
- …
